Wetting contact angle is a measure of the wettability of a mineral. When the liquid is wet on the solid surface, an annular contact line surrounded by three phases of solid, liquid, and gas is formed. This line is also called the three-phase wetting periphery, and every point on this side is the wet contact point. By making a tangent from any point, you can get a balanced contact angle (shown below). There are three surface tensions at this point. It is obvious that the sum of the surface tensions at the air interface (σ _solid-liquid + σ _liquid-gas • cos θ) is balanced. therefore:

Where θ—the surface wetting contact angle of the mineral;
Σ—the surface tension at the interface.
As can be seen from the above formula, the larger the difference of "σ _solid-gas- σ _{solid- liquid} ", the larger the cos θ, and the smaller the θ, the better the mineral wettability, the stronger the hydrophilicity, and the lower the floatability. On the contrary, the smaller the σ _solid-gas- σ _{solid- liquid} difference is, the smaller the cos θ is, and the larger θ is, the poor wettability of the mineral, the strong hydrophobicity, and the good floatability. The cos θ value can also be referred to as the "wetness" of the mineral. It was determined that the contact angle of a mineral rarely more than 90 ° of several common minerals wetting contact angle is: sulfur 80 °, graphite 60 °, galena 47 °, pyrite 33 °, calcite 23 °, quartz 0 to 4°, mica 0°. It can be seen that the contact angle size is generally consistent with the order of floatability known in general flotation experience.
Certain flotation agents can alter and adjust the wettability of the mineral surface. If oleic acid (C ₁₄ H ₃₃ COOH) is adsorbed on the surface of scheelite (CaWO ₄ ), its surface changes from hydrophilic to hydrophobic. This is because the polar group of the oleic acid molecule, COOH, interacts with the calcium ions in the scheelite crystal lattice, and then adheres to the mineral surface. The non-polar C ₁₇ H ₃₃ — (hydrophobic part) of the oleic acid molecule faces water. Therefore, the surface of the scheelite forms a hydrophobic surface. In addition, the surface of the pure galena is treated with an ethyl xanthate collector . When the dose is gradually increased, the contact angle can be increased to about 60°.

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